In all the applications above, there is a need of representing assemblies of digitally-modeled objects which show components which are normally hidden inside the assembly. For instance, it may be necessary to provide a representation of a car wherein the engine or other mechanical organs are visible (“revealed”) through the body of the car.
In order to obtain this kind of graphical representation, it is known to use three-dimensional (3D) digital models of the assembly and of the hidden parts to be revealed, typically created using CAD software, to generate two-dimensional (2D) images thereof, and then to overlay these images in a 2D computer graphics software, using one or more masks to select the regions of interest, wherein the “hidden” part are revealed. This method is cumbersome and requires significant manual intervention from a user. Moreover, if the point of view from which the assembly is seen is changed, it is necessary to repeat the whole process.
An alternative approach operates directly in 3D, by prioritizing internal objects so that they are visible even when they are located behind other objects. For instance, FIG. 1 shows a graphical representation of a toy car (on the left), and of its transmission (on the right). In a “normal” representation of the car, the transmission is mostly hidden, as it lies behind the body and the front-left wheel of the car. However, the transmission can be identified as taking priority over the body and the wheels, and therefore can be seen by transparency in the final, post-processed image (see FIG. 2). The problem with this approach is that it is not possible to make the transmission visible only through specific regions of the body (or, conversely, to make visible only specific parts of the transmission).